The electricity meter is one of the devices that have conventionally been passively controlled but recently been required to perform active control using a data processing device including a central processing unit (CPU).
In the conventional electricity meter, the data processing device has been required to perform the function of measuring and recording the consumed amount of electric power generated by a power company and supplied through a power grid to each house, as well as the function of transmitting to the power company the recorded amount of power consumption through a predetermined communication line.
As for the electricity meter used for next-generation power grids, the data processing device is required not only to perform processing for measuring the amount of electric power distributed from the power company but also to perform processing such as processing for conducting reverse-power-flow control under which electric power from a power generation system such as photovoltaic cell or from a power storage system installed in each house is fed back to the power grid, as well as processing for offsetting the amount of distributed electric power and the amount of electric power fed back to the power grid.
Even a system like the electricity meter is required to reduce as much as possible the electric power consumed by the electricity meter itself. Regarding the data processing device performing the processing as described above, the period during which the data processing device is in the standby state is relatively longer than the period during which the data processing device is performing processing. It is therefore necessary to reduce not only the power consumption of the period during which the data processing device is performing processing but also the power consumption of the period during which the data processing device is in the standby state.
In order to minimize the power consumption of the data processing device in the standby state, the data processing device in the standby state is switched to a low power consumption state. For achieving this low power consumption state, it is necessary not only to stop supply of electric power to functional units including the central processing unit (CPU) and stop an oscillator which generates an operation clock in the data processing device, but also to reduce the power consumption of a power supply circuit itself in the data processing device.